The fission yeast NIMA kinase Fin1p is required for spindle function and nuclear envelope integrity

NIMA kinases appear to be the least functionally conserved mitotic regulators, being implicated in chromosome condensation in fungi and in spindle function in metazoans. We demonstrate here that the fission yeast NIMA homologue, Fin1p, can induce profound chromosome condensation in the absence of the condensin and topoisomerase II, indicating that Finlp-induced condensation differs from mitotic condensation. Fin1p expression is transcriptionally and post-translationally cell cycle-regulated, with Fin1p kinase activity maximal from the metaphase-anaphase transition to G₁. Fin1p is localized to the spindle pole body and fin1Δ cells are hypersensitive to anti-microtubule drugs, synthetically lethal with a number of spindle mutants and require the spindle checkpoint for viability. Moreover, fin1Δ cells show unusual and extensive elaborations of the nuclear envelope. These data support a role for Fin1p in spindle function and nuclear envelope transactions at or after the metaphase-anaphase transition that may be generally applicable to other NIMA-family members.